Exhaust mufflers for large stationary industrial engines are typically designed with reactive and/or dissipative components. Reactive components function by creating a mismatch in acoustic impedance that causes a portion of an acoustic wave to be reflected. The impedance mismatch is typically created by a sudden area change (either an expansion or contraction) in the muffler chamber. When the acoustic wave is reflected, the reflected wave interferes with the incoming wave in accordance with the law of superposition and can thereby “cancel out” a portion of the sound energy.
Dissipative components, on the other hand, employ sound absorbing materials which function by converting acoustic energy into heat energy. Their performance is dependent upon the thickness, density, flow resistivity, and length of the sound absorbing material in the flow path.
Heretofore, for a given engine exhaust pipe diameter, the techniques used in the art for improving the performance of an exhaust muffler in a large industrial application have typically involved increasing the length of the muffler housing and adding additional interior chambers. However, this approach becomes very costly as the length and complexity of the muffler increase. Further, as the length of the muffler unit increases, the muffler takes up more and more space which could be used for other purposes, or which may not be available without moving or modifying other equipment. Moreover, the current technique of simply increasing the length of the muffler and adding additional chambers often does not provide the degree of sound attenuation needed.
A need therefore exists for an improved exhaust muffler for industrial engines which: (a) provides better performance than existing systems over a wider range of frequencies; (b) is of significantly reduced length; (c) is readily adaptable for use with engines of increasing size without significantly increasing the length of the muffler housing; (d) allows the production of more standardized muffler units which can each be used for a range of different engines in a variety of applications; and (e) is less costly and simpler to build, install and maintain.